Basically, during the civil war a bunch of miners under the command of General Ambrose Burnside dug a tunnel underneath a confederate fort, and then blew it up.
actually met some of the escapees, in paris, several years ago now. it's not a smart idea to lock up a bunch of mining engineers in an old jail... (iirc they used plastic coca-cola bottles [la leche negra del imperialismo!], end to end, to make a pipe down which they pumped air to breath; they also had rails and a trolley).
Have there been any cases of them actually being unmanned? It seems cheaper and easier to hire / coerce someone to fly them. Search Google Images for "marijuana ultralight" for some example images of a crashed hang glider trike ultralight (probably due to the massively overweight payload).
I don't know, but an unmanned, no radio, pre-programmed electric ultralight in the middle of nowhere can be very stealthy. Almost no sound signature, difficult to detect radar signature and pretty much invisible at night time. Some small model that could carry 100L and 50kg would be very profitable item.
Well, electric ultralights are still largely prototypes (although a quick Googling makes it look like production units may be available soon). They're definitely not quiet though -- electric motors are quieter than gasoline, but at that size they still make noise. I can't speak as to the radar signature of ultralights. An ultralight that could carry a 50kg payload would be at least the size of a small powered hang glider trike, if we assume negligible weight allowance for the control system and a payload capacity equivalent to the weight of an average human pilot.
For a small stream of deliveries, perhaps. And the costs and risks of loss would seem to be fairly linear with an aircraft strategy.
The tunnel has large start-up costs but then tiny marginal costs for bulk transport. Beyond a certain expected lifetime, it'd surely dominate aerial costs/risks for cost-effectiveness.
If so, http://www.businessweek.com/articles/2012-08-02/the-narco-tu... is a way beter read.